Precise visualization of catheters and needles, and real-time knowledge of their localization with respect to the anatomy, are needed for minimally invasive interventions. Intra-operative ultrasound is often used for these purposes.
However, many surgical tools are difficult to image with conventional pulse-echo ultrasound. Also, visualization is often incomplete or artefact-prone.
For instance, the usability of 3D Transoesophagial Echocardiography (3D-TEE) for guidance of catheter cardiac interventions is still limited because it is challenging to image catheters reliably with ultrasound.
Catheters and needles are specular reflectors that reflect the sound away from the imaging probe if the insonifying angles are not favorable.
As a consequence, a catheter appears on and off on 3D-TEE images during its progression through the cardiac chambers. It also frequently happens that some parts of the catheter are visible and others not depending on the local angle between the catheter and the imaging beams. For instance the distal end of the catheter may be invisible and some point along its shaft may be mistaken as its tip. Also, due to weak reflection, signal from the catheter may be drowned in signal from the surrounding anatomy.
It is also difficult to image intravenous catheters.
Likewise, needles, often used for biopsy, nerve block, drug delivery, hyperthermic therapy, and radiofrequency (RF) ablation, etc., are hard to visualize, especially when thin and applied to deep tissue locations. Visibility greatly improves if the insonifying angle is perpendicular to the needle. However, achieving a favorable angle is usually limited to shallow needle insertions. In addition, due to tissue heterogeneities and asymmetric needle bevel, the needle often deviates from its planned trajectory, even when a needle guide is used. If the needle deviates from the imaged plane, it becomes invisible. Very often, the clinician jiggles the needle to see on the image display where it is located.
Electromagnetic (EM) sensors have been attached to the interventional tool and the ultrasound probe, to determine the tool pose, i.e., location and orientation, in the acquired image (SonixGPS Specifications Sheet, UltraSonix, available at the World Wide Web at ultrasonix.com/webfm_send/117).
In a technique proposed in a paper entitled “Enhancement of Needle Visibility in Ultrasound-Guided Percutaneous Procedures, by Cheung et al., Ultrasound in Medicine and Biology, Vol. 30, No. 5 (2004), the ultrasound probe is used to determine the tool pose. Beamforming parameters are created, based on the determination, to insonify the tool at a better angle.